A direct current motor, which is a kind of direct current rotating electrical machine, includes a stator, an armature, commutators, and brushes. Generally, the stator has a yoke case and a magnet. The armature and the commutator are fixed to an outer peripheral portion of a rotating shaft of the direct current motor to form a rotator. The brush is fixed to the stator side to supply direct current to the rotator. The brushes are often held by a brush holder mounted to an opening of the yoke case. The commutator receives the direct current through the brushes to switch the direction of the current flowing in armature coils. Consequently, continuous torque is generated in the armature, and the rotator rotates.
The brush makes a mechanical sliding contact with the commutator, and the polarity is frequently switched depending on the rotation speed of the rotator. Thus, spark discharge occurs in the sliding contact portion of the brush and the commutator, and electromagnetic noise occurs due to impulse voltage caused by the spark discharge. In order to restrain the electromagnetic noise influencing an electric circuit located in the vicinity of the direct current motor, a noise filter is often provided in a circuit that connects the brushes with the direct current source. FIG. 11A shows an example of a circuit in which a capacitor C1, connected in parallel with the direct current source VM, is provided as a noise filter. FIG. 11B shows another example of a circuit, in which the capacitor C1 and choke coils L (L1, L2) are provided. In the example, the capacitor C1 is connected in parallel with the direct current source VM, and the choke coils L (L1, L2) are connected in series with electric power supply lines of the positive and negative electrodes.
When a comparison is made with the same motors, an amount and energy of the electromagnetic noise vary depending on an operation environment such as the load or the rotation speed of the motor. Further, the effect on a circuit caused by the electromagnetic noise varies depending on an environment that the motor is located. For example, the effect on a circuit caused by the electromagnetic noise varies depending on whether another electric circuit is located in the vicinity of the direct current motor, or whether a member such as a metal plate, serving as a shield against the electromagnetic noise, is located in the vicinity of the direct current motor. Hence, the noise filter including the choke coils, shown in FIG. 11B, is not always necessary, and the configuration of the noise filter should be selected according to the operation and locating environments. In case of a component such as the capacitor C1, which is connected in parallel with the circuit (the direct current source VM), it would be easy to determine whether or not to mount the component on the circuit at the time of production. On the other hand, if a component such as the choke coil L1 or L2, which is connected in series with the circuit, is not mounted, the circuit is disconnected. In order to avoid the situation, a different kind of brush holder, in particular, a different kind of terminal, needs to be used.
In JP 2003-79109A, a brush holder is proposed in view of the above circumstances. A noise filter using the choke coils, which is similar to that of FIG. 1B, may be mounted in the brush holder. In addition, whether or not to mount the choke coils may be determined at the time of the production. According to JP 2003-79109A, the brush holder is configured so as to accommodate a current carrying member, either a terminal plate or the choke coil, in each choke coil accommodating portion of the brush holder. Since the terminal plate functions as a conducting path, the circuit shown in FIG. 11A is formed by mounting the terminal plates to the circuit configured as shown in FIG. 11B, instead of the choke coils.
The brush holder disclosed in JP 2003-79109A is excellent in that the same brush holder may be used irrespective of the presence or absence of the choke coils. However, a disadvantage lies in the fact that when the choke coils are not needed and the cost and the man hours may be saved, the terminal plates need to be mounted in the brush holder. The cost of the terminal plates is required and the man hours are not reduced. Consequently, the reduction effect of the production cost is limited. The similar disadvantage occurs in the direct current dynamo which is a kind of the direct current rotating electrical machine.
A need exists for a brush holder which is not susceptible to the drawback mentioned above.